WO2018131051A1

WO2018131051A1 - Combined-cycle power generation thermodynamic system

Info

Publication number: WO2018131051A1
Application number: PCT/IN2017/050598
Authority: WO
Inventors: Mahesh Lakshminarayanan; Pardeep GARG; Prashant Kumar
Original assignee: Mahesh Lakshminarayanan; Garg Pardeep
Priority date: 2017-01-11
Filing date: 2017-12-15
Publication date: 2018-07-19

Abstract

The embodiments herein provide a system and a method for power generation using combined cycle technology with two power blocks. A part of the heat available in a first working media in a first power block after expansion is used to heat a second working media in a second power block using a heat recovery unit and the remaining heat is internally recuperated within the first power block. The working media comprises oxygen rich media and burnt fuel in the first power block and carbon dioxide and/or other mixtures in the second power block. The selection of these media, the architectural configurations and the operating conditions lead to a substantial increase in overall efficiency of the combined cycle technology thereby approaching the thermodynamic efficiency limit.

Description

COMBINED-CYCLE POWER GENERATION THERMODYNAMIC SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The embodiments herein claim the priority of the Indian Provisional Patent Application (PPA) filed on January 11, 2017 with the serial number 201741001107 and the subsequent Indian Non-Provisional Patent Application (NPA) filed on October 31, 2017 with the title, "PEAK EFFICIENCY MULTI-TURBINE GAS-BASED COMBINED-CYCLE POWER GENERATION THERMODYNAMIC SYSTEM", and the contents of which are included in entirety as reference herein.

BACKGROUND

Technical Field

[0002] The embodiments herein are generally related to the field of power generation. The embodiments herein are particularly related to a system and a method for power generation using combined cycle technology. The embodiments herein are more particularly related to a system and a method for power generation operated at the efficiency closer to the thermodynamic limit using two power blocks in a combined cycle configuration.

Description of the Related Art

[0003] The conventional power plants based on gas turbine (Bray ton cycle) or steam turbine (Rankine cycle) technologies, in general, use fossil fuel as a primary energy source for power generation. With increasing population and human living standards in the recent years, there is a multi-fold increase in the capacity of such power plants resulting in a faster depletion of the finite fossil-based energy resources along with an increase in carbon emissions. Power generation using renewable energy sources such as solar or wind seldom hold the promise to displace the conventional fossil fuel based power generation methods to meet a base load or peak load demands in a reliable manner. Under such scenarios, achieving higher efficiencies in the fossil fuel based power generation plants becomes the only available alternative.

[0004] The currently available methods and systems based on fossil fuel for power generation are operated at efficiencies much lower than what the upper thermodynamic limit allows. When the conventional thermodynamic cycles such as air based gas Brayton and steam based Rankine cycles are used independently, they offer thermal efficiency in the range of 30-40 %. However, their combination (air Brayton and steam Rankine) offers 50-60 % efficiency depending upon operating temperature. This combined technology is known as combined cycle gas turbine (CCGT).

[0005] In this technology, the exhaust heat from the fuel fired gas turbine cycle is used to boil the pressurized water into high enthalpy steam in a heat recovery unit, also known as a heat recovery steam generator (HRSG). The exergy based thermodynamic analysis of CCGT with HRSG reveals that there is large exergy destruction in the HRSG due to the occurrence of large and non-uniform temperature difference across the warm and the cold fluid in it, which is primarily due to the phase change of pressurized water during boiling. This limits the overall efficiency of the CCGT based technologies.

[0006] In the prior art, ammonia-water mixture has been used to recover heat from the hot gas to remove heat more gradually as compared to the steam-based heat recovery systems and methods, thereby slightly improving energy efficiencies when compared to CCGT, but the increase is not large enough to offset additional capital costs and complexity of operation of this arrangement.

[0007] Conventionally, steam is also used as a medium to generate electricity from the waste heat sources. These systems are in general bulky due to large volumetric flow rates the turbine exhaust; and there is a need to realize waste heat to power solutions that are compact. Over the past decade, supercritical C0₂ (S-C0₂) cycles have gained popularity and are being perceived as an alternate to the steam based power solutions for power generation. There is also mention of the use of S-C0₂ cycle for utilizing waste heat sources. In these applications, S-C0₂ cycle is considered in isolation and in most of the cases, the classical definition of efficiency is used to present the performance of waste heat solution which is ratio of electricity generated to heat received by the cycle. Given the fact that there is not much temperature drop during the expansion of S-C0₂, a substantial amount of heat is recuperated within the S-C0₂ cycle. The ratio of heat internally recovered/recuperated to the electricity produced could be as high as 5 in a S-C0₂ cycle. This leaves a lot of external heat unutilized and results in the mismatch between the available waste-heat versus waste -heat actually used. If the definition of efficiency is slightly modified to the ratio of electricity generated to the waste heat available, S-C0₂ cycle equipped with a single expansion process turns out be a highly inefficient proposition. [0008] Moreover, S-C0₂ is used as independent power block in nuclear and solar applications. There is also mention of S-CO₂ being used in the top cycle and air in the bottoming cycle. This configuration, however, does not lead to significant improvements in the efficiency when compared to the conventional CCGT.

[0009] There also exist S-CO₂ cycles equipped with multiple expansion processes occurring along distinct isentropes in the prior art which are capable of recovering the waste heat with a reasonable temperature drop in the waste heat stream. However, these cycles have a number of issues such as high temperature gradients during recuperation process leading to irreversible heat transfer. Also, the effect of heat transfer near critical point is transferred to the waste heat recovery unit resulting in large temperature gradients inside the heat recovery heat exchangers. Further, as the temperature of the available waste heat increases, the more difficult it becomes to tailor an efficient S-CO₂ power block that can recover the reasonable amount of waste heat generating the least irreversibility. Further, there is also mention about the need of pressures as high as 400 bar in order to recover a reasonable amount of heat from the waste heat source. This exhibits the inefficiency of the manner in which S-CO₂ cycles are mentioned to be coupled to conventional gas turbine systems. The overall efficiency of conventional CCGT system or the gas turbine units with supercritical media as proposed in the literature remains roughly similar to what the conventional CCGTs offer today.

[0010] Hence, there is a need for a system and a method for power generation using a high efficiency combined cycle technology with two power blocks to convert thermal energy into mechanical energy which can operate closer to the thermodynamic limit. There is also a need for a system and method using power cycle designs or configurations that minimize exergy destruction during heat exchange processes pushing the cycle efficiencies thus closer to thermodynamic limit. There is also a need for a system and method for power generation providing controlled temperature differential during heat exchanger processes to achieve an increased in the overall efficiency of the power generation, thus approaching towards the thermodynamic efficiency limit. There is also a need for a system and method for realizing an efficient coupling of the gas turbine unit with the S-CO₂ cycle that generates less entropy.

[0011] The above-mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification. OBJECTS OF THE EMBODIMENTS HEREIN

[0012] The primary object of the embodiments herein to provide a system and method for power generation using a high efficiency combined cycle technology with two power blocks to convert chemical/thermal energy into mechanical energy.

[0013] Another object of the embodiments herein to provide a system and method for enabling the waste heat recovery process in a first power block instead of a second power block.

[0014] Yet another object of the embodiments herein to provide a system and method for power generation for enabling the two power blocks to interact with each other using a heat recovery unit in such a manner that the exhaust of the first power block on a first low pressure side transfers a part of heat to the second power block and the heat which is not transmitted to the second power block is internally recovered within the first power block.

[0015] Yet another object of the embodiments herein to provide a system and method for power generation by using oxygen rich media and burnt fuel in the first power block with carbon dioxide and/or other mixtures in the second power block as the working media.

[0016] Yet another object of the embodiments herein to provide a system and method using power cycle architectures or thermodynamic configurations to minimize exergy destruction during heat transfer within the system thereby achieving efficiencies closer to the thermodynamic limit.

[0017] Yet another object of the embodiments herein to provide a system and method for power generation to provide a controlled temperature differential during heat transfer within the system thereby resulting in an increased efficiency that approaches the thermodynamic limit.

[0018] Yet another object of the embodiments herein to provide a power cycle configuration that utilizes the chemical energy stored in a fuel in most efficient way to achieve efficiencies closer to the thermodynamic limit and to minimize entropy generation/irreversibility during heat transfer within the system by minimizing a difference between temperature gradient at the hot end and the cold end of heat exchangers employed in the system.

[0019] Yet another object of the embodiments herein to provide a system and method for power generation wherein the second working media does not undergo a phase change in any part of second power block and thus operates in Brayton cycle configuration. [0020] Yet another object of the embodiments herein to provide a system and method for power generation wherein the second working media in the second power block involves a phase change during heat rejection and/or heat addition process similar to steam Rankine cycle.

[0021] Yet another object of the embodiments herein to provide a system and method for power generation that effectively transfers the heat from the first working media to the second working media through a heat recovery unit.

[0022] Yet another object of the embodiments herein to provide a system and method for power generation that minimizes difference between temperature gradient at a hot end and temperature gradient at a cold end of heat exchangers employed within the system to result in lower irreversibility generation.

[0023] Yet another object of the embodiments herein to provide a system and method for power generation with the first power block operating at more than two pressure sides.

[0024] Yet another object of the embodiments herein to provide a system and method for power generation with the second power block operating at more than two pressure sides.

[0025] Yet another object of the embodiments herein to provide a system and method for power generation that minimizes the variation in the ratio of specific heats of a hot stream and a cold stream as the heat transfer takes place in any of the heat exchangers within the system by appropriately configuring the thermodynamic architecture.

[0026] Yet another object of the embodiments herein to provide a system and method for power generation that comprises at least one cooler to cool the second working media.

[0027] Yet another object of the embodiments herein to provide a system and method for power generation that offers an efficient way for coupling the gas turbine unit to another Brayton cycle.

[0028] Yet another object of the embodiments herein to provide a system and method for power generation that reduces the exhaust heat temperatures in an efficient way by recovering the heat within the system.

[0029] These and other objects and advantages of the embodiments herein will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings. SUMMARY

[0030] The various embodiments herein provide a combined cycle system for power generation. According to an embodiment herein, a combined cycle system for power generation is provided. The system comprises a first power block and a second first power block.

[0031] According to an embodiment herein, the first power block is configured for generating mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working fluid circuit. The first power block is divided into at least two pressure sides that include a first low pressure side and a first high pressure side. The first working media is circulated through the first low pressure side and the first high pressure side in the first power block.

[0032] According to an embodiment herein, the second power block is configured for generating mechanical energy using heat recovered from the heat recovery unit in a closed loop circuit. A second working media is circulated in the closed loop circuit. The second power block is divided into at least two pressure sides that include a second high pressure side and a second low pressure side.

[0033] According to an embodiment herein, the first power block further comprises a first compression unit comprising at least one compressor, a first recuperation unit comprising at least one recuperator, a combustion unit having at least one combustor on the first high pressure side, a first expansion unit comprising at least one expander, and a heat recovery unit comprising at least one heat exchanger having a hot end and a cold end.

[0034] According to an embodiment herein, the first compression unit is connected between the first low pressure side and the first high pressure side to pressurise the first working media.

[0035] According to an embodiment herein, at least one recuperator of the first recuperation unit is configured to preheat the pressurized first working media on the first high pressure side using the heat available on the first low pressure side of the first power block. The at least one recuperator of the first recuperation unit is provided with a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C.

[0036] According to an embodiment herein, the at least one combustor of the combustion unit is configured to receive the preheated first working media and the fuel to discharge a combustion product stream in a temperature range of 600 °C to 2000 °C. [0037] According to an embodiment herein, the first expansion unit is connected between the first low pressure side and the first high pressure side and is configured to expand the combustion product stream.

[0038] According to an embodiment herein, the at least one heat exchanger of the heat recovery unit is configured to receive and recover heat from expanded combustion product stream. The heat exchanger is further configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the cold end below 40°C.

[0039] According to an embodiment herein, the second power block further comprises a second expansion unit comprising at least one expander, a second recuperation unit comprising at least one recuperator, a cooling unit comprising at least one cooler, and a second compression unit comprising at least one compressor.

[0040] According to an embodiment herein, the second expansion unit is connected between the second high pressure side and the second low pressure side and is configured to expand the second working media available on the second high pressure side.

[0041] According to an embodiment herein, the recuperator of the second recuperation unit is configured to cool the second working media on the second low pressure side and to preheat the second working media on the second high pressure side. The at least one recuperator of the second recuperation unit has a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C.

[0042] According to an embodiment herein, the cooler of the cooling unit is configured to cool the second working media.

[0043] According to an embodiment herein, the second compression unit is connected between the second low pressure side and the second high pressure side to pressurise the second working media.

[0044] According to an embodiment herein, the first compression unit comprises a plurality of compressors operating in series or parallel. The first compression unit is configured to perform an inter-cooling operation, and wherein the first compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the heat recovery unit. [0045] According to an embodiment herein, the second compression unit comprises a plurality of compressors operating in series or parallel. The second compression unit is configured to perform an inter-cooling operation, and wherein the second compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the second recuperation unit.

[0046] According to an embodiment herein, a flow regulation unit is configured to regulate a flow of one or more media. The media is selected from a group consisting of the first working media, the combustion product stream, and the second working media.

[0047] According to an embodiment herein, the flow regulation unit is configured to split the combustion product stream into a first stream and a second stream. The first stream is used to preheat the first working media available on the first high pressure side in the first recuperation unit. The second stream is used to preheat a part of the second working media in the heat recovery unit.

[0048] According to an embodiment herein, the flow regulation unit is further configured to split the second working media on the second high pressure side into a first stream and a second stream. The first stream is preheated in the second recuperation unit and the second stream is preheated in the heat recovery unit.

[0049] According to an embodiment herein, the fuel comprises one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

[0050] According to an embodiment herein, the combustion unit is configured to receive oxygen for combustion from one or both the first working media and the fuel.

[0051] According to an embodiment herein, the second working media comprises a fluid containing carbon dioxide.

[0052] According to an embodiment herein, the first expansion unit comprises a plurality of expanders operating in series or parallel. The first expansion unit is configured to perform a reheating operation between the pluralities of expanders.

[0053] According to an embodiment herein, the second expansion unit comprises a plurality of expanders operating in series or parallel. The second expansion unit is configured to perform a reheating operation between the pluralities of expanders.

[0054] According to an embodiment herein, the first compression unit and the second compression unit are operated at a pressure ratio within a range of 1.01 to 50.

[0055] According to an embodiment herein, the first working media is added with a polar chemical compound. [0056] According to an embodiment herein, the first power block is configured as an open loop circuit or a semi-closed loop circuit to circulate the first working media, wherein the first working media comprises a fluid containing oxygen or carbon dioxide.

[0057] According to an embodiment herein, a combined cycle method for power generation is provided. The method comprises the following steps. A first power block is configured for circulating a first working media to generate mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working media circuit. The first power block is divided into at least two pressure sides that include a first low pressure side and a first high pressure side. The first working media is circulated through the first low pressure side and the first high pressure side in the first power block. The first working media is pressurized in a first compression unit connected between the first low pressure side and the first high pressure side. The first compression unit is provided with at least one compressor. The pressurized first working media on the first high pressure side is preheated and the first working media on the first low pressure side is cooled in at least one recuperator of a first recuperation unit. The at least one recuperator is provided with a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C. The preheated first working media is received and the fuel is combusted in at least combustor of a combustion unit on the first high pressure side to discharge a combustion product stream at a temperature range of 600°C to 2000°C. The combustion product stream is expanded to generate mechanical energy in the first expansion unit connected between the first high pressure side and the first low pressure side of the first block. The first expansion unit comprises at least one expander. The heat is recovered from the expanded combustion product stream in at least one heat exchanger of a heat recovery unit. The at least one heat exchanger has a hot end and a cold end so that the heat exchanger is configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the colder end below 40°C.

[0058] According to an embodiment herein, a second power block is configured for circulating a second working media in a closed loop circuit to generate mechanical energy using heat recovered from the heat recovery unit. The second working media is circulated in the closed loop circuit. The second power block is divided into at least two pressure sides that include a second high pressure side and a second low pressure side. The second working media is expanded to generate mechanical energy in a second expansion unit connected between the second high pressure side and the second low pressure side. The second expansion unit comprises at least one expander. The expanded second working media on the second low pressure side is cooled in at least one recuperator of a second recuperation unit. In turn, the second working media on the second high pressure side is preheated in the at least one recuperator of the second recuperation unit. The at least one recuperator has a hot end and a cold end, so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C. The second working media is cooled in a cooling unit having at least one cooler. The second working media is pressurized in a second compression unit connected between the second low pressure side and the second high pressure side. The second compression unit comprises at least one compressor.

[0059] According to an embodiment herein, the method further comprises pressurizing the first working media with a plurality of compressors in the first compression unit. The plurality of compressors is operated in series or parallel. The first compression unit is configured to perform an inter-cooling operation between the pluralities of compressors and wherein the first compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the heat recovery unit.

[0060] According to an embodiment herein, the method further comprises pressurizing the second working media with a plurality of compressors in the second compression unit. The plurality of compressors is operated in series or parallel. The second compression unit is configured to perform an inter-cooling operation between the pluralities of compressors and wherein the second compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the second recuperation unit.

[0061] According to an embodiment herein, the method further comprises regulating the flow of one or more media. The one or more media is selected from a group consisting of the first working media, the combustion product stream and the second working media.

[0062] According to an embodiment herein, the method further comprises splitting the combustion product stream into a first stream and a second stream using the flow regulation unit. The first stream is used for preheating the first working media in the first recuperation unit and the second stream is used for preheating a part of the second working media in the heat recovery unit. [0063] According to an embodiment herein, the method further comprises splitting the second working media on the second high pressure side into a first stream and a second stream using the flow regulation unit. The first stream is preheated in the second recuperation unit and the second stream is preheated in the heat recovery unit.

[0064] According to an embodiment herein, the method further comprises combusting the fuel containing one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

[0065] According to an embodiment herein, oxygen is supplied to the combustion unit through one or both the first working media and the fuel.

[0066] According to an embodiment herein, the second working media comprises a fluid containing carbon dioxide.

[0067] According to an embodiment herein, the method further comprises expanding the first working media in a plurality of expanders in the first expansion unit. The plurality of expanders is operated in series or parallel. The first expansion unit is configured to perform reheating operation between the pluralities of expanders.

[0068] According to an embodiment herein, the method further comprises expanding the second working media in a plurality of expanders in the second expansion unit. The plurality of expanders is operated in series or parallel. The second expansion unit is configured to perform a reheating operation between the pluralities of expanders.

[0069] According to an embodiment herein, the method further comprises operating the first compression unit and the second compression unit at pressure ratios within a range of 1.01 to 100.

[0070] According to an embodiment herein, the method further comprises adding a polar chemical compound to the first working media circulated in the first power block.

[0071] According to an embodiment herein, the method further comprises operating the first power block in an open loop to circulate the first working media containing oxygen or in a semi-closed loop to circulate the first working media containing carbon dioxide.

[0072] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating the preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:

[0074] FIG. 1A illustrates a block diagram of a combined cycle system, according to one embodiment herein.

[0075] FIG. IB illustrates a block diagram of a combined cycle system provided with a first high pressure side, a first low pressure side and a first intermediate pressure side in the first power block along with a second high pressure side, a second low pressure side and a second intermediate pressure side in the second power block of the combined cycle system, according to one embodiment herein.

[0076] FIG. 1C illustrates a block diagram of a combined cycle system indicating a first working media circuit and a second working media circuit, according to one embodiment herein.

[0077] FIG. 2 illustrates a block circuit diagram of a combined cycle system, according to one embodiment herein.

[0078] FIG. 3 illustrates a block circuit diagram of a combined cycle system, indicating an exemplary combined cycle system, according to one embodiment herein.

[0079] FIG. 4 illustrates a block circuit diagram of a combined cycle system, indicating another example of combined cycle system, according to one embodiment herein.

[0080] FIG. 5 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein.

[0081] FIG. 6 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein.

[0082] FIG. 7 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein.

[0083] FIG. 8 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein. [0084] FIG. 9 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein.

[0085] Although the specific features of the embodiments herein are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the embodiments herein.

DETAILED DESCRIPTION OF THE EMBODIMENTS HEREIN

[0086] In the following detailed description, a reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical, and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.

[0087] The embodiments herein provide a combined cycle system for power generation. According to an embodiment herein, a combined cycle system for power generation is provided. The system comprises a first power block and a second first power block.

[0088] According to an embodiment herein, the first power block is configured for generating mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working media circuit. The first power block is divided into at least two pressure sides that include a first low pressure side and a first high pressure side. The first working media is circulated through the first low pressure side and the first high pressure side in the first power block.

[0089] According to an embodiment herein, the second power block is configured for generating mechanical energy using heat recovered from a heat recovery unit in a closed loop circuit. A second working media is circulated in the closed loop circuit. The second power block is divided into at least two pressure sides that include a second high pressure side and a second low pressure side.

[0090] According to an embodiment herein, the first power block further comprises a first compression unit comprising at least one compressor, a first recuperation unit comprising at least one recuperator, a combustion unit having at least one combustor on the first high pressure side, a first expansion unit comprising at least one expander, and a heat recovery unit comprising at least one heat exchanger having a hot end and a cold end. [0091] According to an embodiment herein, the first compression unit is connected between the first low pressure side and the first high pressure side to pressurise the first working media.

[0092] According to an embodiment herein, the at least one recuperator of the first recuperation unit is configured to preheat the pressurized first working media on the first high pressure side using the heat available on the first low pressure side of the first power block. The at least one recuperator is provided with a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C.

[0093] According to an embodiment herein, the at least one combustor of the combustion unit is configured to receive the preheated first working media and the fuel to discharge a combustion product stream in a temperature range of 600 °C to 2000 °C.

[0094] According to an embodiment herein, the first expansion unit is connected between the first high pressure side and the first low pressure side and is configured to expand the combustion product stream.

[0095] According to an embodiment herein, the at least one heat exchanger of the heat recovery unit is configured to receive and recover heat from the expanded combustion product stream. The at least one heat exchanger of the heat recovery unit is further configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the colder end below 40°C.

[0096] According to an embodiment herein, the second power block further comprises a second expansion unit comprising at least one expander, a second recuperation unit comprising at least one recuperator, a cooling unit having at least one cooler configured for cooling the second working media, and a second compression unit comprising at least one compressor.

[0097] According to an embodiment herein, the second expansion unit is connected between the second high pressure side and the second low pressure side to expand the second working media available on the second high pressure side.

[0098] According to an embodiment herein, the at least one recuperator of the second recuperation unit is configured to cool the second working media available on the second low pressure side and to preheat the second working media available on the second high pressure side. The at least one recuperator of the second recuperation unit has a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C. [0099] According to an embodiment herein, the second compression unit is connected between the second low pressure side and the second high pressure side to pressurize the second working media.

[00100] According to an embodiment herein, the first compression unit comprises a plurality of compressors operating in series or parallel. The first compression unit is configured to perform an inter-cooling operation between the pluralities of compressors and wherein the first compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the heat recovery unit.

[00101] According to an embodiment herein, the second compression unit comprises a plurality of compressors operating in series or parallel. The second compression unit is configured to perform an inter-cooling operation between the pluralities of compressors, and wherein the second compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the second recuperation unit.

[00102] According to an embodiment herein, a flow regulation unit is configured to regulate the flow of one or more media. The media is selected from a group consisting of the first working media, the combustion product stream and the second working media.

[00103] According to an embodiment herein, the flow regulation unit is configured to split the combustion product stream into a first stream and a second stream. The first stream is used to preheat the first working media in the first recuperation unit. The second stream is used to preheat a part of the second working media in the heat recovery unit.

[00104] According to an embodiment herein, the flow regulation unit is further configured to split the second working media on the second high pressure side into a first stream and a second stream. The first stream is preheated in the second recuperation unit and the second stream is preheated in the heat recovery unit.

[00105] According to an embodiment herein, the fuel comprises one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

[00106] According to an embodiment herein, the combustion unit is configured to receive oxygen required for combustion from one or both, the first working media and the fuel. [00107] According to an embodiment herein, the second working media comprises a fluid containing carbon dioxide.

[00108] According to an embodiment herein, the first expansion unit comprises a plurality of expanders operating in series or parallel. The first expansion unit is configured to perform a reheating operation between the pluralities of expanders.

[00109] According to an embodiment herein, the second expansion unit comprises of a plurality of expanders operating in series or parallel. The second expansion unit is configured to perform a reheating operation between the pluralities of expanders.

[00110] According to an embodiment herein, the first compression unit and the second compression unit are operated at a pressure ratio within a range of 1.01 to 50.

[00111] According to an embodiment herein, the first working media is added with a polar chemical compound.

[00112] According to an embodiment herein, the first power block is configured as an open loop circuit to circulate the first working media comprising a fluid containing oxygen or as a semi-closed loop circuit to circulate the first working media comprising a fluid containing carbon dioxide.

[00113] According to an embodiment herein, the system further comprises the second power block that operates in a semi-closed loop configured with at least one combustor of the combustion unit in the second power block.

[00114] According to an embodiment herein, a combined cycle method for power generation is provided. The method comprises the following steps. A first power block is configured for circulating a first working media to generate mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working fluid circuit. The first power block is divided into at least two pressure sides that include a first low pressure side and a first high pressure side. The first working fluid is circulated through the first low pressure side and the first high pressure side in the first power block. The first working media is pressurized in a first compression unit connected between the first low pressure side and the first high pressure side. The first compression unit is provided with at least one compressor. The pressurized first working media on the first high pressure side is preheated using the heat available on the first low pressure side in at least one recuperator of a first recuperation unit. The at least one recuperator is provided with a hot end and a cold end so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C. The preheated first working media is received and the fuel is combusted in at least one combustor of a combustion unit provided on the first high pressure side to discharge a combustion product stream at a temperature range of 600°C to 2000°C. The combustion product stream is expanded to generate mechanical energy in a first expansion unit connected between the first high pressure side and the first low pressure side. The first expansion unit comprises at least one expander. The heat is recovered from the expanded combustion product stream in at least one heat exchanger of a heat recovery unit. The at least one heat exchanger has a hot end and a cold end so that the heat exchanger is configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the cold end below 40°C.

[00115] According to an embodiment herein, a second power block is configured for circulating a second working media in a closed loop circuit to generate mechanical energy using heat recovered in the heat recovery unit. The second working media is circulated in the closed loop circuit. The second power block is divided into at least two pressure sides that include a second high pressure side and a second low pressure side. The second working media is expanded to generate mechanical energy in a second expansion unit connected between the second high pressure side and the second low pressure side. The second expansion unit comprises at least one expander. The expanded second working media on the second low pressure side is cooled in at least one recuperator of a second recuperation unit and wherein the second working media is available on the second high pressure side in turn is preheated. The at least one recuperator of the second recuperation unit has a hot end and a cold end, so that a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C. The second working media is cooled in a cooling unit having at least one cooler. The second working media is pressurized in a second compression unit connected between the second low pressure side and the second high pressure side. The second compression unit comprises at least one compressor.

[00116] According to an embodiment herein, the method further comprises pressurizing the first working media with a plurality of compressors in the first compression unit. The plurality of compressors is operated in series or parallel. The first compression unit is configured to perform an inter-cooling operation between the pluralities of compressors and wherein the first compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the heat recovery unit. [00117] According to an embodiment herein, the method further comprises pressurizing the second working media with a plurality of compressors in the second compression unit. The plurality of compressors is operated in series or parallel. The second compression unit is configured to perform an inter-cooling operation between the pluralities of compressors and wherein the second compression unit is configured to perform an intercooling operation between the pluralities of compressors to supply heat to the second working media in the second recuperation unit.

[00118] According to an embodiment herein, the method further comprises regulating the flow of one or more media. The media is selected from a group consisting of the first working media, the combustion product stream and the second working media.

[00119] According to an embodiment herein, the method further comprises splitting the combustion product stream into a first stream and a second stream using a flow regulation unit. The first stream is used for preheating the first working media in the first recuperation unit and the second stream is used for preheating a part of the second working media in the heat recovery unit.

[00120] According to an embodiment herein, the method further comprises splitting the second working media into a first stream and a second stream using the flow regulation unit. The first stream is preheated in the second recuperation unit. The second stream is preheated in the heat recovery unit.

[00121] According to an embodiment herein, the method further comprises combusting the fuel containing one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

[00122] According to an embodiment herein, oxygen is supplied to the combustion unit through one or both, the first working media and the fuel.

[00123] According to an embodiment herein, the second working media comprises a fluid containing carbon dioxide.

[00124] According to an embodiment herein, the method further comprises expanding the first working media in a plurality of expanders in the first expansion unit. The plurality of expanders is operated in series or parallel. The first expansion unit is configured to perform reheating operation between the pluralities of expanders.

[00125] According to an embodiment herein, the method further comprises expanding the second working media in a plurality of expanders in the second expansion unit. The plurality of expanders is operated in series or parallel. The second expansion unit is configured to perform a reheating operation between the pluralities of expanders. [00126] According to an embodiment herein, the method further comprises operating the first compression unit and the second compression unit at pressure ratios within a range of 1.01 to 100.

[00127] According to an embodiment herein, the method further comprises adding a polar chemical compound to the first working media circulated in the first power block.

[00128] According to an embodiment herein, the method further comprises operating the first power block in an open loop or in a semi-closed loop to circulate the first working media containing oxygen or carbon dioxide.

[00129] According to an embodiment herein, the method further comprises operating the second power block in a semi-closed loop configured with at least one combustor of the combustion unit in the second power block.

[00130] The various embodiments herein provide a system and method for power generation using combined cycle technology with two power blocks, namely, a first power block and a second power block. The two power blocks interact using a heat recovery unit wherein the first expansion unit exhaust (turbine exhaust) of the first power block transfers a part of heat to the second power block. Here, a part of the heat available in a the combustion product stream in the first power block after expansion is used to heat a second working media in the second power block using the heat recovery unit and the remaining heat is internally recuperated within the first power block. Thus, the waste heat (exhaust of the first power block turbine or the exhaust of the first expansion unit) is utilized in both the blocks (cycles); partly in the first power block and partly in the second power block.

[00131] The system and method comprise oxygen rich media and burnt fuel in the first power block and carbon dioxide (C0₂) and/or other mixtures in the second power block as the working media. The specific choice of these media and the operating conditions leads to controlled temperature differential in the heat exchangers resulting in an increased overall efficiency of the combined cycle technology and thus approaching the upper thermodynamic efficiency limit.

[00132] According to one embodiment herein, a thermodynamic configuration using two Brayton cycles involving air and supercritical C0₂ in the first power block and the second power block, respectively is proposed. Use of these media in the first power block and the second power block is capable of increasing heat to electricity conversion efficiencies as high as 10% when compared to the conventional combined cycle through mitigating scope for irreversible heat transfer in all the heat exchanger units used in the system. This configuration thus maximizes the potential of the gradual and orderly heat transfer in all the heat exchangers. With this configuration the further scope for cycle efficiency enhancement can only be realized by improving the turbo-machinery efficiencies.

[00133] According to one embodiment herein, the residual heat which is not transmitted to the second power block is regenerated in the first power block cycle in a gradual and orderly manner. This leads to a method of power generation wherein the scope of entropy generation due to heat transfer is reduced to a significantly lower value thus getting closer to the efficiency limit specified by 2^nd law of thermodynamics. This provides the thermodynamic architecture a highest peak in the landscape of technologies formed by various possible combined cycle technologies.

[00134] According to one embodiment herein, a system and method for power generation using a high efficiency combined cycle technology to convert thermal energy into mechanical/electrical energy is provided. The system comprises two working fluid circuits circulating a first working media, a second working media and a heat recovery unit for establishing thermal connection between the two said fluid circuits.

[00135] According to one embodiment herein, the first working fluid circuit, referred to as a first power block comprises a first compression system configured for increasing a pressure of the first working media from a low pressure level to a high pressure level; and a first recuperation unit fluidly connected to the high pressure outlet of the first compression unit. The first recuperation unit is configured for utilizing heat from the exhaust of the heat recovery unit within the first power block. The first power block also comprises a combustion unit in fluid communication with the first recuperation unit and configured for heating the first working media using the heat of combustion of fuel; and a first expansion unit arranged between the high and low pressure side of the first working media and fluidly connected to a heat recovery unit. The second working fluid circuit, referred to as a second power block, is in thermal communication with the first power block through the heat recovery unit configured to heat the second working media using a part of the heat available at the exhaust of the first expansion unit of the first power block. The second power block comprises a second expansion unit arranged between a high pressure level and a low pressure level maintained in the second power block configured for receiving and expanding the heated second working media discharged from the outlet of the heat recovery unit. The term 'level' should be interchangeably read as 'side' in context of defining the pressure sides or levels. [00136] According to one embodiment herein, the second power block also comprises a second recuperation unit fluidly connected to the low pressure outlet of the second expansion unit and configured for transferring heat from the low pressure exhaust of the second expansion unit. The second power block further comprises a cooling unit fluidly connected to the second recuperation unit and configured for cooling the second working media received from the low pressure outlet of the second recuperation unit employing dry- or wet-cooling mechanism and a second compression unit fluidly connected to the cooling unit and configured for increasing the pressure of the second working media from the low pressure level to the high pressure level. .

[00137] According to one embodiment herein, the system and method is further configured for exploiting various thermodynamic states of the second working media in the second power block. Here, the second working media does not undergo phase change in any part of second power cycle, thus operating in Brayton cycle configuration. Thus, the second working media operates in supercritical state (both, the low pressure level and the high pressure level of the second working media are above the critical pressure of the second working media), transcritical state (only the high pressure level of second working media is higher than the critical pressure of the second working media), subcritical state (both, the low pressure level and the high pressure level of the second working media are lower than the critical pressure of the second working media).

[00138] According to one embodiment herein, the second working media in the second power block involves a phase change during heat rejection and/or heat addition process, similar to steam Rankine cycle.

[00139] According to one embodiment herein, the system is configured for transferring increased amount of heat from the combustion product stream to the second working media through the heat recovery unit in order to eliminate the first expansion unit from the first power block thereby transferring all the heat of combustion available in the first working media or in the combustion product stream to the second working media.

[00140] According to one embodiment herein, the system and method is configured for regulating the amount of heat transferred to the second working media by controlling the amount of mass flow through the first expansion unit in the first power block. This comprises placing a flow regulation unit which comprises of a flow divider valve (FDV) in a fluidly connected way between the high pressure level and the low pressure level of the first expansion unit in parallel facilitating a part of the first working media to bypass the first expansion device through a throttle valve. [00141] According to one embodiment herein, the second power block employs a recuperation effect carried out in a second recuperation unit that comprises two recuperators. The mass flow rates of the second working media are divided in two streams using a flow regulation unit (also referred to as FDV) and the divided streams of the second working media are pressurized to a high pressure level in a compression unit comprising two compressors. The division of the mass flow rates of the second working media using the flow regulation unit (also referred to as FDV) provides minimum temperature differential during heat exchange process in the recuperation unit across the low pressure level and the high pressure level second working media resulting in lower irreversibility generation and thus higher power generation efficiency.

[00142] According to one embodiment herein, the second power block is operated at three pressure levels referred to as a high pressure level, an intermediate pressure level and a low pressure level. The outlet of the expansion unit is at the low pressure level, while the cooling effect is carried out at the intermediate pressure level which is determined by the ambient conditions. This lowers the high pressure requirement in the second power block but provides large temperature differential in one of the recuperator.

[00143] According to one embodiment herein, the system minimizes the temperature differential across a recuperation unit, comprising two recuperators while the low pressure requirement in the second power block is maintained. This comprises division of the mass flow rate of the second working media at the intermediate pressure level using an FDV. This leads to minimum temperature differential during heat exchange process in the recuperation unit across the low pressure level and the high pressure level second working media resulting in lower irreversibility generation and thus higher power generation efficiency. Additionally, a cooler is provided to further cool the second working media at the low pressure level resulting in a lower compression work involved in pressurizing second working fluid from the lower pressure level to the intermediate pressure level.

[00144] According to one embodiment herein, a fuel-based combined cycle technology system and method are provided. The description highlights several embodiments of the invention provided mainly as examples to better describe the disclosure without limiting the scope of the invention. These embodiments describe different configurations, arrangements, features and methods along with various figures to schematically describe them. The embodiments are frequently referred to each other, which by itself do not constitute a relationship between them. Moreover, it is possible to combine the features or parts of one embodiment with that of another embodiment in different ways without deviating from the scope of this disclosure.

[00145] Also, certain terminologies and naming conventions have been used throughout this description. As one skilled in the art may appreciate, it is possible to use different names to refer to the same idea or feature, which will not limit the scope of the invention, unless specifically mentioned otherwise. The functionality of the various parts of the embodiments should be assigned importance over the names by which they are referred to, as the names by themselves are meant only for differentiation. Numerical values stated in this disclosure may be approximate or exact unless otherwise mentioned specifically and the various embodiments may deviate from the stated numbers without deviating from the intended scope.

[00146] FIG. 1A illustrates a block diagram of a combined cycle system, according to one embodiment herein. With respect to FIG. l, the combined cycle system 100 comprises two power blocks, known as a first power block 101 and a second power block 105. The first power block 101 generates mechanical energy using heat of combustion of a fuel in a Brayton cycle circulating a first working media. The first power block 101 has at least two pressure sides that include a first low pressure side 103 and a first high pressure side 102. The first power block 101 comprises a first compression unit 111 having at least one compressor. The first compression unit 111 is configured to pressurize the first working media from the first low pressure side 103 to the first high pressure side 102. A first recuperation unit 121 has at least one recuperator. The at least one recuperator of the first recuperation unit 121 is configured to preheat the pressurized first working media on the first high pressure side 102 using heat available in the first low pressure side 103 of the first power block 101. Further, a combustion unit 131 has at least one combustor. The at least one combustor of the combustion unit 131 is configured to receive the preheated first working media along with the fuel. The said combustion unit 131 converts the chemical energy of the fuel to heat energy thereby heating the first working media and discharging a combined mass as a combustion product stream at a temperature range of 600 °C to 2000 °C. A first expansion unit 141 has at least one expander. The first expansion unit 141 is configured to expand the combustion product stream from the first high pressure side 102 to the first low pressure side 103 for generating mechanical energy. The mechanical energy generated in the first expansion unit 141 may also be converted to electrical energy. Further, a heat recovery unit 151 has at least one heat exchanger. The at least one heat exchanger is configured to recover heat from the combustion product stream available on the first low pressure side 103 of the first power block 101.

[00147] According to one embodiment herein, the second power block 105 of the combined cycle system 100 circulating a second working media in a closed loop generates mechanical energy using heat recovered from the heat recovery unit 151. The second power block 105 has at least two pressure sides that include a second low pressure side 107 and a second high pressure side 106. A second expansion unit 161 has at least one expander, and wherein the second expansion unit 161 is configured to expand the second working media from the second high pressure side 106 to the second low pressure side 107 for generating mechanical energy. The mechanical energy generated in the second expansion unit 161 is also converted to electrical energy. A second recuperation unit 171 has at least one recuperator. The at least one recuperator of the second recuperation unit 171 is configured for cooling the expanded second working media available on the second low pressure side 107 by rejecting the heat to the second working media available on the second high pressure side 106. Further, a cooling unit 181 having at least one cooler is configured to cool the second working media circulating in the second power block 105. A second compression unit 191 has at least one compressor. The second compression unit 191 is configured to pressurise the second working media from the second low pressure side 107 to the second high pressure side 106.

[00148] According to one embodiment herein, each one of the recuperators in the first recuperation unit 121 has a hot end and a cold end and wherein the difference between the temperature gradients at the hot end and the cold end is maintained below 80 °C. The at least one heat exchangers in the heat recovery unit 131 has a hot end and a cold end. The difference between the temperature gradients at the hot end and the cold end of the at least one heat exchanger of the heat recovery unit 131 is maintained below 40 °C. The at least one of the recuperator in the second recuperation unit 171 has a hot end and a cold end. The difference between the temperature gradients at the hot end and the cold end of the at least one recuperator of the second recuperation unit is maintained below 80 °C. The term temperature gradient is defined as the difference in temperature between a hot stream and a cold stream exchanging heat at the given point of a recuperator or a heat exchanger. [00149] According to one embodiment herein, the first compression unit 111 or/and the second compression unit 191 comprise a single stage or multi-stage compressors(s) or pumps operating in series or parallel. In case, where multi-stage compressors are used, the inter-cooling operation is provided or not provided in between the stages and the said cooling is wet or dry.

[00150] According to one embodiment herein, the first expansion unit 141 or/and the second expansion unit 161 comprise single or multi-stage expanders operated in series or parallel. The first expansion unit 141 or/and the second expansion unit 161 comprise one or more expanders selected from a group consisting of centrifugal type of turbines, aero derivative turbines, and positive displacement expanders. In case of multi-stage expansion, reheating facility is provided or not provided between the stages, and the reheating is achieved by using a part of the heat available in the combustion unit 131 or by having an additional combustor in the combustion unit 131.

[00151] According to one embodiment herein, the fuel comprises one or more elements/compounds selected from a group consisting of carbonaceous origin, hydrogen and oxygen. According to one embodiment herein, the second working media in the second power block 105 is carbon-dioxide as the sole component or mixed with one or more organic fluids such as but not limited to alkanes, alkenes and alkynes.

[00152] According to one embodiment herein, the first power block 101 is an open loop and the first working media comprises a fluid containing oxygen including but not limited to air. The oxygen component of the first working fluid assists in the combustion of the fuel in the combustion unit 131 to convert chemical energy to heat energy. If more than one recuperator is used in the first recuperation unit 121 or/and the second recuperation unit 171, or if more than one heat exchanger is used in the heat recovery unit 151, or if more than one compressor is used in the first compression unit 111 or the second compression unit 191, or if more than one cooler is used in the cooling unit 181, a flow regulation unit 136 (not shown in FIG. 1A) is also provided appropriately within the first power block 101 or/and the second power block 105 to regulate or control the flow of the one or more of the fluids selected from a group consisting of the first working media, the combustion product stream and the second working media. The flow regulation unit 136 further comprises flow unit 136 comprising flow regulators, flow controllers, flow dividers, pressure relief valves or any such device for regulating, controlling or dividing the flow of the one or more fluids selected from the group consisting of the first working media, the combustion product stream and the second working media. The regulated flow helps in redistributing energy from excess to deficient areas of the first power block 101 and/or the second power block 105, thereby controlling the difference in temperature gradients in the heat recovery unit 151 and/or the first recuperation unit 121 and/or the second recuperation unit 171 of the combined cycle system 100.

[00153] According to one embodiment herein, the process of capturing carbon dioxide or other similar gases produced during the combustion process is also coupled with the combined cycle disclosed in the invention. According to one embodiment herein, the first power block 101 is an open loop and the combustion product stream made available at an outlet of the first recuperation unit on the first low pressure side of the first power block 101 is post treated for capturing carbon dioxide.

[00154] According to one embodiment herein, the first power block 101 is an open loop and the fuel is pre-treated using an oxygen rich stream for partially oxidizing or reforming the fuel before supplying to the first power block 101.

[00155] According to one embodiment herein, the first power block 101 is a semi- closed loop and the first working media comprises a fluid containing carbon dioxide. The use of carbon dioxide in media comprises a fluid containing carbon dioxide. The use of carbon dioxide in the first working media is carried out in a thermodynamic cycle that operates in either Brayton or transcritical or Rankine cycle mode. Further, the carbon dioxide generated in the combustion unit 131 is expanded instead of being pressurized to produce a cooling effect.

[00156] According to one embodiment herein, both, the first working media and the second working media comprise a fluid containing carbon dioxide. Further, one or more media in the group formed by the first working media, the second working media and the combustion product stream is mixed with each other at the appropriate thermodynamic stages of the combined cycle system. In such cases, the thermodynamic processes in the first power block and the second power block is combined and carried out in a cascaded manner.

[00157] According to one embodiment herein, the first working media and the fuel are oxidised in the presence of oxygen using an electro-chemical reaction. Further, the first working media and/or the combustion product stream are configured to undergo changes in chemical and physical properties while circulating in the first power block 101 by adding a polar chemical compound such as water to the first working media or the combustion product stream. Further, the heat available in the combined cycle system 100 is utilized for providing the heat to the additive or the fuel. [00158] According to one embodiment herein, the heat available from the first power block 101 and/or the second power block 105 is utilized in the processes related to organic Rankine cycle, thermal desalination, cooling or any such applications.

[00159] According to one embodiment herein, the first compression unit 111 and the second compression unit 191 are operated at pressure ratios within the range of 1.01 to 100.

[00160] FIG. IB illustrates a block diagram of a combined cycle system provided with a first high pressure side 102, a first low pressure side 103 and a first intermediate pressure side 104 in the first power block 101 and the second high pressure side 106, a second low pressure side 107 and a second intermediate pressure side 108 in the second power block 105 of combined cycle system 100, according to one embodiment herein. With respect to FIG. IB, the first high pressure side 102, the first low pressure side 103 and the first intermediate pressure side 104 in the first power block 101, and the second high pressure side 106, the second low pressure side 107 and the second intermediate pressure side 108 in the second power block 105 are marked using dotted lines.

[00161] FIG. 1C illustrates a block diagram of a combined cycle system indicating a first working media circuit and a second working media circuit, according to one embodiment herein. With respect to FIG. 1C, the flow of the first working media (along with the combustion product stream) and the second working media through the combined cycle system is depicted using dotted lines with arrows.

[00162] FIG. 2 illustrates a block circuit diagram of a combined cycle system 200, according to one embodiment herein. With respect to FIG. 2, the first power block 201 comprises a first low pressure side 103 and a first high pressure side 102. A compressor 112 in the first compression unit 111 pressurizes the first working media and delivers to the first high pressure side. The first working media is received and preheated by a recuperator 122 of the first recuperation unit 121. The preheated first working media is sent to a combustor 132 of the combustion unit 131 to discharge the combustion product stream. The combustion product stream is expanded in an expander 142 of the first expansion unit 141 delivering the combustion product stream to the first low pressure side 103. A heat exchanger 152 of the heat recovery unit 151 receives and cools the expanded combustion product stream, which is then sent to the first low pressure side 103 of the recuperator 122 of the first recuperation unit 121 for further cooling. The cooled combustion product stream is vented or used for any application. The heat recovered from the heat exchanger 152 of the heat recovery unit 151 is utilized to heat the second working media in the second power block having a second high pressure side 106 and a second low pressure side 107. The heated second working media on the second high pressure side 106 is expanded in an expander 162 of the second expansion unit 161 and delivered to the second low pressure side 107. The expanded second working media is cooled in a recuperator 172 of the second recuperation unit 171 before being sent to a cooler 182 of the cooling unit 181. The cooled second working media is pressurized in a compressor 192 of the second compression unit 191 and delivered to the high pressure side of the recuperator 172 of the second recuperation unit 171 for preheating. The pre -heated second working media is delivered to the high pressure side of the heat exchanger 152 of the heat recovery unit 151 to complete the loop.

[00163] According to one embodiment herein, the second power block is configured in such a way that the second working media is operated in any thermodynamic regime in reference to the critical point of the second working media, namely supercritical, transcritical or subcritical states.

[00164] According to one embodiment herein, the combined cycle system is configured to throttle a part of the combustion product stream across the first expansion unit 141 or to operate in the absence of the first expansion unit 141.

[00165] FIG. 3 illustrates a block circuit diagram of a combined cycle system, indicating an exemplary combined cycle system, according to one embodiment herein. With respect to FIG. 3, the second working media exiting the expander 162 of the second expansion unit 161 is cooled in two recuperators 172 and 374 connected in series in the second recuperation unit 171. The second working media exiting the second recuperation unit 171 is divided into two streams using a flow regulator 336 of the flow regulation unit 136. The first stream is compressed in a compressor 394 of the second compression unit 191 and the second stream is cooled in a cooler 182 of the cooling unit 181. The second stream is further pressurized in compressor 192 of the compression unit 191 before being preheated in the recuperator 374 of the second recuperation unit 171. Subsequently, the second stream is merged with the pressurized first stream from the compressor 394 of the second compression unit 191 and further heated in the recuperator 172 of the second recuperation unit 171.

[00166] FIG. 4 illustrates a block circuit diagram of a combined cycle system, indicating another example of combined cycle system, according to one embodiment herein. With respect to FIG. 4, the second power block 405 comprises three pressure sides, namely, a second low pressure side 107, a second intermediate pressure side 108 and a second high pressure side 106 as depicted in Fig. IB. The second compression unit 191 is configured to operate in multi-stages with an inter-cooling operation provided between a compressor 192 and a compressor 494 of the second compression unit 191. The heat available in the inter- cooling operation is recuperated within the second power block 405 using a recuperator 374 of the second recuperation unit 171. The second working media exiting the expander 162 of the second expansion unit 161 is cooled in recuperator 172 of the second recuperation unit 171, before being sent to the compressor 192 of the second compression unit 191. The second working media exits the compressor 192 of the second compression unit 191 on to the second intermediate pressure side 108 and is further cooled in the recuperator 374 of the second recuperation unit 171, before being cooled again in the cooler 182 of the cooling unit 181. The second working media exiting the cooling unit is pressurized in the compressor 494 of the compression unit 191 and delivered on to the second high pressure side 106 before being preheated in series in the recuperators 374 and 172 of the second recuperation unit 171.

[00167] FIG. 5 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein. With respect to FIG. 5, the second power block 505 comprises three pressure sides, namely, a second low pressure side 107, a second intermediate pressure side 108 and a second high pressure side 106. The second working media exiting the expander 162 of the second expansion unit 161 is cooled in two recuperators 172 and 374 connected in series in the second recuperation unit 171. The second working media exiting the second recuperation unit 171 is pressurized in the compressor 192 of the second compression unit 191 and delivered on to the second intermediate pressure side 108. The second working media available on the second intermediate pressure side 108 is divided into two streams using a flow regulator 536 of the flow regulation unit 136. The first stream is compressed in a compressor 594 of the second compression unit 191 and delivered on to the high pressure side while the second stream is cooled in a cooler 182 of the cooling unit 181. The second stream is further pressurized in compressor 494 of the compression unit 191 and delivered on to the high pressure side for preheating in the recuperator 374 of the second recuperation unit 171. Subsequently the second stream is merged with the pressurized first stream from the compressor 594 of the second compression unit 191 and further heated in the recuperator 172 of the second recuperation unit 171.

[00168] FIG. 6 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein. With respect to FIG.6, the second power block 605 comprises a cooler 684 of the cooling unit 181 operating on the second low pressure side 107 to lower the work of compression in the compressor 494 of the second compression unit 191. [00169] FIG. 7 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein. With respect to FIG.7, the combustion product stream available at the outlet of the expander 142 of the first expansion unit 141 is cooled in heat exchanger 152 of the heat recovery unit 151. Subsequently, the combustion product stream is divided into two streams using a flow regulator 736 of the flow regulation unit 136. The two streams comprise a first stream and a second stream. The first stream is sent to the recuperator 122 of the first recuperation unit 121 for cooling. The second stream passes through heat exchanger 754 of the heat recovery unit 151 for cooling. The second working media available at the outlet of the compressor 192 of the second compression unit 191 is divided into two streams called a third stream and fourth stream using a flow regulator 737 of the flow regulation unit 136. The third stream is preheated in the recuperator 172 of the second recuperation unit 171. The fourth stream is heated in the heat exchanger 754 of the heat recovery unit 151 and subsequently merged with the preheated third stream.

[00170] FIG. 8 illustrates a block circuit diagram of a combined cycle system, indicating yet another example of combined cycle system, according to one embodiment herein. With respect to FIG.8, the first power block 801 comprises three pressure sides known as the first low pressure side 103, the first intermediate pressure side 104 and the first high pressure side 102. The first compression unit 191 is configured for operation in multi- stages with an inter-cooling operation provided between a compressor 112 and a compressor 814 of the first compression unit 111. The heat available in the inter-cooling operation is supplied for heating the second working media in the second power block 805 using a heat exchanger 754 of the heat recovery unit 151. The first working media is pressurized in a compressor 112 of the first compression unit 111 from the first low pressure side 103 to the first intermediate pressure side 104 before being sent to a heat exchanger 754 of the heat recovery unit 151 for cooling. The first working media available at the outlet of the heat exchanger 754 is sent to a compressor 814 for further pressurizing the first working media to the first high pressure side 102. The second working media available at the outlet of the compressor 192 of the second compression unit 191 is heated in the heat exchanger 754 of the heat recovery unit 151 before being sent to the recuperator 172 of the second recuperation unit 171 for further heating. The second working media exiting the second recuperation unit 171 on the second high pressure side 106 is further heated in the heat exchanger 152 of the heat recovery unit 151. [00171] It may also be appreciated by those skilled in the art that features of the disclosed embodiments may be combined to realize various new embodiments. For example, when the features of embodiment presented in FIG. 6 are integrated to the embodiment present in FIG. 7, the embodiment presented in FIG. 9 is realized.

[00172] With respect to FIG. 9, the second power block 905 comprises three pressure side; a second low pressure side 107, a second intermediate pressure side 108, and a second high pressure side 106. The combustion product stream available at the outlet of the first expansion unit 141 is cooled in a heat exchanger 152 of the heat recovery unit 151. Subsequently, the combustion product stream is divided into two streams using a flow regulator 936 of the flow regulation unit 136, called a first stream and a second stream. The first stream is sent to the recuperator 122 of the first recuperation unit 121 for cooling. The second stream passes through heat exchanger 954 of the heat recovery unit 151 for cooling. The second working media made available at the outlet of the second expansion unit 161 is cooled in three stages before being pressurized in a compressor 994 of the second compression unit 191. The second working media made available at the outlet of the second expansion unit 161 is cooled firstly in a recuperator 172 of the second recuperation unit 171, secondly in a recuperator 974 of the second recuperation unit 171 and thirdly in a cooler 182 of the cooling unit 181. The second working media made available at the second intermediate pressure side 108 is divided into a third stream and a fourth stream using a flow regulator 937 of the flow regulation unit 136. While the third stream is pressurized using a compressor 192 of the compression unit 191, the fourth stream undergoes a three stage process before the third stream and the fourth stream are merged on the second high pressure side. The fourth stream is firstly cooled in a cooler 984 of the cooling unit 181, secondly pressurized in a pump 996 of the second compression unit 191 and thirdly preheated in the recuperator 974 of the second recuperation unit 171. The merged second working media on the second high pressure side 106 is further divided into a fifth stream and a sixth stream using a flow regulator 938 of the flow regulation unit 136. While the fifth stream is preheated in a recuperator 172 of the second recuperation unit 171, the sixth stream is heated in the heat exchanger 954 of the heat recovery unit 151. The preheated fifth stream and the heated sixth stream are merged and sent to the heat exchanger 152 of the heat recovery unit 151 for further heating.

[00173] It may also be appreciated by those skilled in the art that the excess heat available in the first power block can be used for other similar processes such as but not limited to heating up the fuel without deviating from the spirit of the present disclosure to achieve similar objectives. Similarly, the second power block can receive the deficient heat from the external processes such as but not limited to processes related to carbon capture and storage and coal gasification without deviating from the spirit of the present disclosure to achieve similar objectives.

[00174] The embodiments herein disclosed above deliver a significant improvement in performance efficiency over the best available conventional combined cycle gas turbine systems operating with steam in the bottom cycle. A table showing such improvements for different classes of architecture modifications is shown in Table 1 below:

[00175] Table 1: Improvement in efficiency of energy conversion of the various embodiments over the conventional combined cycle gas turbine (CCGT) systems operating with steam in the bottom cycle:

[00176] The variables contributing to performance improvement are broadly grouped as follows: number of heat exchangers in the heat recovery unit (1 or 2), presence of flow regulation in the first power block, presence of flow regulation in the second power block, and more than two pressure sides in the second power block. Each variable contributes to a higher overall performance efficiency, while the effect of some variables being higher than that of others. These variables are coupled with each other to realize further improvements in the performance efficiency. The Table 1 highlights the range of efficiency improvements that are realized when one of the above variables is fixed and the remaining are allowed to vary. When the number of heat exchangers in the heat recovery unit is fixed as one, then a system having a flow regulation unit in the first power block exhibits an efficiency improvement in the range of 1-6%, the performance range being a consequence of the variation allowed in the second power block with respect to number of pressure sides and presence of the flow regulation unit. It is to be noted that the above chart discloses/teaches only the possible improvements in performance efficiencies over and above a conventional combined cycle system involving a gas turbine in the first power block and steam turbine in the second power block. For example, when the said conventional combined cycle system delivers an efficiency of 60% subject to operating conditions, then the invention disclosed here with its various embodiments is configured to yield an absolute efficiency in range of 60-74%.

[00177] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

[00178] The embodiments herein provide a system and method for power generation with high fuel-to-electricity efficiency using combined cycle technology comprising two power blocks. This technology helps approaching the thermodynamic limit of efficiency.

[00179] Another advantage of the embodiments herein the compactness of the system. The disclosed combined cycle system incurs a low volumetric flow rate throughout the thermodynamic cycle by avoiding sub-atmospheric pressures which are inevitable in the conventional combined cycle systems. The high power densities of power generation in the disclosed combined cycle system opens up the possibility of using this technology not only in the stationary applications but also in the mobile applications such as but not limited to aviation and marine. The combined cycle technology is also perceived to be a capital efficient scheme of power generation as the bill of material associated with the material of construction can be significantly brought down owing to higher power densities.

[00180] In many regions of the world such as India where the demand of natural has is high but the supply is limited, the application of conventional combined cycle (gas turbine with steam Rankine cycle) is limited to peak load applications only. With higher operational efficiency, the application of the disclosed combined cycle technology can be extended to meeting the based load demands. [00181] The embodiments herein offers both the capital and the operational cost advantages. These advantages are highly likely to result in the reduced cost of electricity.

[00182] The embodiments herein also reveals the system and the method for significantly reducing the carbon emissions associated with the conventional systems and methods of power generation.

[00183] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such as specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments.

[00184] It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modifications. However, all such modifications are deemed to be within the scope of the claims.

Claims

CLAIMS What is claimed is:

1. A combined cycle system for power generation, the system comprising:

a first power block for generating mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working media circuit, and wherein the first power block is divided into at least two pressure sides, and wherein the at least two pressure sides comprise a first low pressure side and a first high pressure side, and wherein the first working fluid is circulated through the first low pressure side and the first high pressure side in the first power block, and wherein the first power block further comprises:

a first compression unit comprising at least one compressor, and wherein the first compression unit is connected between the first low pressure side and the first high pressure side to pressurise the first working media;

a first recuperation unit comprising at least one recuperator, wherein the at least one recuperator is configured to preheat the pressurized first working media on the first high pressure side using the heat available on the first low pressure side, and wherein each recuperator is provided with a hot end and a cold end, and wherein a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C;

a combustion unit having at least one combustor on the first high pressure side, and wherein the at least one combustor is configured to receive the preheated first working media and the fuel to discharge a combustion product stream at a temperature range of 600 °C to 2000 °C;

a first expansion unit comprising at least one expander, and wherein the first expansion unit is connected between the first high pressure side and the first low pressure side, to expand the combustion product stream;

a heat recovery unit comprising at least one heat exchanger having a hot end and a cold end, and wherein the at least one heat exchanger is configured to receive and recover heat from expanded combustion product stream, and wherein the at least one heat exchanger is further configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the cold end below 40°C;

a second power block generating mechanical energy using heat recovered from the heat recovery unit in a closed loop circuit, and wherein a second working media is circulated in the closed loop circuit, and wherein the second power block is divided into at least two pressure sides, and wherein the at least two pressure sides comprise a second high pressure side and a second low pressure side, and wherein the second power block further comprises:

a second expansion unit comprising at least one expander, wherein the second expansion unit is connected between the second high pressure side and the second low pressure side, to expand the second working media available on the second high pressure side;

a second recuperation unit comprising at least one recuperator, and wherein the at least one recuperator is configured to cool the second working media on the second low pressure side and to preheat the pressurized second working media on the second high pressure side, and wherein each recuperator has a hot end and a cold end, and wherein a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C;

a cooling unit having at least one cooler configured for cooling the second working media; and

a second compression unit comprising at least one compressor, and wherein the second compression unit is connected between the second low pressure side and the second high pressure side to pressurize the second working media.

2. The system according to claim 1, wherein the first compression unit comprises a plurality of compressors operating in series or parallel and wherein the first compression unit is configured to perform an inter-cooling operation, and wherein the first compression unit is configured to perform an inter-cooling operation between the plurality of compressors to supply heat to the second working media in the heat recovery unit.

3. The system according to claim 1, wherein the second compression unit comprises a plurality of compressors operating in series or parallel and wherein the second compression unit is configured to perform an inter-cooling operation, and wherein the second compression unit is configured to perform an inter-cooling operation between the plurality of compressors to supply heat to the second working media in the second recuperation unit.

4. The system according to claim 1, wherein a flow regulation unit is configured to regulate a flow of one or more media, and wherein the one or more media is selected from a group consisting of the first working media, the combustion product stream and the second working media.

5. The system according to claim 4, wherein the flow regulation unit is configured to split the combustion product stream into a first stream and a second stream, and wherein the first stream is used to preheat the first working media in the first recuperation unit, and wherein the second stream is used to preheat a part of the second working media in the heat recovery unit.

6. The system according to claim 4, wherein the flow regulation unit is further configured to split the second working media on the second high pressure side into a first stream and a second stream, and wherein the first stream is preheated in the second recuperation unit, and wherein the second stream is preheated in the heat recovery unit.

7. The system according to claim 1, wherein the fuel comprises one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

8. The system according to claim 1, wherein the combustion unit is configured to receive oxygen for combustion from one or both the first working media and the fuel.

9. The system according to claim 1, wherein the second working media comprises a fluid containing carbon dioxide.

10. The system according to claim 1, wherein the first expansion unit comprises a plurality of expanders operating in series or parallel, and wherein the first expansion unit is configured to perform a reheating operation between the plurality of expanders.

11. The system according to claim 1, wherein the second expansion unit comprises of a plurality of expanders operating in series or parallel, and wherein the second expansion unit is configured to perform a reheating operation between the plurality of expanders.

12. The system according to claim 1, wherein the first compression unit and the second compression unit are operated at a pressure ratio within a range of 1.01 to 100.

13. The system according to claim 1, wherein the first working media is added with a polar chemical compound.

14. The system according to claim 1, wherein the first power block is configured as an open loop circuit to circulate the first working media comprises a fluid containing oxygen or a semi-closed loop circuit to circulate the first working media comprises a fluid containing carbon dioxide.

15. A combined cycle method for power generation, the method comprising the steps of:

configuring a first power block for circulating a first working media to generate mechanical energy using heat of combustion of a fuel in a Brayton cycle by circulating a first working media through a first working media circuit, and wherein the first power block is divided into at least two pressure sides, wherein the at least two sides comprise a first low pressure side and a first high pressure side, and wherein the first working media is circulated through the first low pressure side and the first high pressure side in the first power block;

pressurizing the first working media in a first compression unit connected between the first low pressure side and the first high pressure side, and wherein the first compression unit is provided with at least one compressor;

preheating the pressurized first working media on the first high pressure side using the heat available on the first low pressure side in at least one recuperator of a first recuperation unit, and wherein the at least one recuperator is provided with a hot end and a cold end, and wherein a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C;

receiving the preheated first working media and combusting the fuel in at least one combustor of a combustion unit on the first high pressure side to discharge a combustion product stream at a temperature range of 600°C to 2000°C;

expanding the combustion product stream to generate mechanical energy in a first expansion unit comprising at least one expander connected between the first high pressure side and the first low pressure side;

recovering heat from the expanded combustion product stream in at least one heat exchanger of a heat recovery unit, and wherein the at least one heat exchanger has a hot end and a cold end, and wherein the at least one heat exchanger is configured to maintain a difference between a temperature gradient at the hot end and a temperature gradient at the cold end below 40°C;

configuring a second power block for circulating a second working media in a closed loop circuit to generate mechanical energy using heat recovered from the heat recovery unit, and wherein the second working media is circulated in the closed loop circuit, and wherein the second power block is divided into at least two pressure sides, and wherein the at least two pressure sides comprise a second high pressure side and a second low pressure side;

expanding the second working media to generate mechanical energy in a second expansion unit comprising of at least one expander connected between the second high pressure side and the second low pressure side;

cooling the expanded second working media on the second low pressure side and preheating the second working media on the second high pressure side in at least one recuperator of a second recuperation unit, and wherein the at least one recuperator has a hot end and a cold end, and wherein a difference between a temperature gradient at the hot end and a temperature gradient at the cold end is maintained below 80°C;

cooling the second working media in a cooling unit having at least one cooler; and

pressurizing the second working media in a second compression unit connected between the second low pressure side and the second high pressure side and wherein the second compression unit is provided with at least one compressor.

16. The method according to claim 15, further comprises pressurizing the first working media with a plurality of compressors in the first compression unit, and wherein the plurality of compressors are operated in series or parallel and wherein the first compression unit is configured to perform an inter-cooling operation, and wherein the first compression unit is configured to perform an inter-cooling operation between the plurality of compressors to supply heat to the second working media in the heat recovery unit.

17. The method according to claim 15, further comprises pressurizing the second working media with a plurality of compressors in the second compression unit, and wherein the plurality of compressors are operated in series or parallel and wherein the second compression unit is configured to perform an inter-cooling operation, and wherein the second compression unit is configured to perform an inter-cooling operation between the plurality of compressors to supply heat to the second working media in the second recuperation unit.

18. The method according to claim 15, further comprises regulating the flow of one or more media, and wherein the one or more media is selected from a group consisting of the first working media, the combustion product stream and the second working media.

19. The method according to claim 15, further comprises splitting the combustion product stream into a first stream and a second stream using the flow regulation unit, and wherein the first stream is used for preheating the first working media in the first recuperation unit and the second stream is used for preheating a part of the second working media in the heat recovery unit.

20. The method according to claim 15, further comprises splitting the second working media into a first stream and a second stream using the flow regulation unit, and wherein the first stream is preheated in the second recuperation unit, and wherein the second stream is preheated in the heat recovery unit.

21. The method according to claim 15, further comprises combusting the fuel containing one or more compounds selected from a group consisting of carbonaceous material, hydrogen and oxygen.

22. The method according to claim 15, wherein oxygen is supplied to the combustion unit through one or both the first working media and the fuel.

23. The method according to claim 15, wherein the second working media comprises a fluid containing carbon dioxide.

24. The method according to claim 15, further comprises expanding the first working media in a plurality of expanders in the first expansion unit, and wherein the plurality of expanders is operated in series or parallel, and wherein the first expansion unit is configured to perform reheating operation between the plurality of expanders.

25. The method according to claim 15, further comprises expanding the second working media in a plurality of expanders in the second expansion unit, and wherein the plurality of expanders is operated in series or parallel, and wherein the second expansion unit is configured to perform a reheating operation between the plurality of expanders.

26. The method according to claim 15, further comprises operating the first compression unit and the second compression unit at pressure ratios within a range of 1.01 to 100.

27. The method according to claim 15, further comprises adding a polar chemical compound to the first working media circulated in the first power block.

28. The method according to claim 15, further comprises operating the first power block in an open loop to circulate the first working media containing oxygen or in a semi- closed loop to circulate the first working media containing carbon dioxide.